The field of the invention is sensing devices for industrial control systems, and particularly, limit switch devices such as that described in U.S. Pat. Nos. 3,555,215 and 4,103,136.
Such limit switches include an arm, or other mechanical element, which is positioned to make contact with a moving portion of the industrial equipment being controlled. The arm is mechanically coupled to one or more sets of switch contacts and these are opened and closed in response to arm motion. The limit switch contacts may be wired into a control circuit comprised of relays, or they may be wired to the input modules of programmable controllers such as that described in U.S. Pat. No. 4,118,792, or numerical control systems such as that described in U.S. Pat. No. 4,263,647. Characteristically, such limit switches are employed in harsh environments and are required to operate millions of cycles. When a limit switch fails to operate properly, it may require that an entire assembly line be shut down, and thus, durability and reliability are of the utmost importance in limit switch design.